Scroll type fluid displacement apparatus are well known in the prior art. For example, U.S. Pat. No. 801,182 issued to Creux discloses such an apparatus which includes two scrolls, each having a circular end plate and a spiroidal or involute spiral element. The scrolls are maintained angularly and radially offset so that both spiral elements interfit to form a plurality of line contacts between their spiral curved surfaces to thereby seal off and define at least one pair of fluid pockets. The relative orbital motion of the two scrolls shifts the line contacts along the spiral curved surfaces and, as a result, the volume of the fluid pockets increases or decreases, dependent on the direction to the orbital motion. Thus, a scroll type fluid displacement apparatus may be used to compress, expand or pump fluids.
Scroll type fluid displacement apparatus are suitable for use as refrigerant compressors in building air conditioners. In such building air conditioners, thermal control of a room, or control of the air conditioner, is generally accomplished by intermittent operation of the compressor because capacity control mechanisms usually are not provided for the compressors of such air conditioners. Though the energy required for maintaining the room at the desired temperature usually is not large once the desired temperature is first achieved, a relatively large load is required to drive the compressor, at least during initial intermittent operation of the compressor, and to a lesser extent upon each subsequent actuation of the compressor. This intermittent operation wastefully consumes large amounts of energy.
When conventional scroll type compressors are used in automobile air conditioners, these compressors usually are driven by the automobile engine through an electromagnetic clutch. Once the passenger compartment is cooled to the desired temperature, like building air conditioners, control of the output of the compressor usually is accomplished by intermittent operation of the compressor through the electromagnetic clutch. Since a relatively large load is required to drive the compressor, this large load is intermittently applied by the automobile engine. Accordingly, conventional scroll type compressors for automobile air conditioners also wastefully consume large amounts of energy in achieving and maintaining the desired temperature in the passenger compartment.
Recently, it was recognized that it is desirable to provide a scroll type compressor with a displacement or volume adjusting mechanism to control the compression ratio as operation demands. This has been accomplished by various mechanisms which control the volume of the sealed off pockets. Mechanisms to control the volume of the sealed off pockets generally have used a pair of holes through the end plate of one of the scrolls, with the pair of holes providing controlled communication to a chamber located on the opposite side of the scroll end plate. For example, in U.S. Pat. No. 4,468,178 issued on Aug. 28, 1984 to Masaharu Hiraga et al. the pair of holes provides communication to the suction chamber, while in U.S. Pat. No. 4,505,651 issued on Mar. 19, 1985 to Kiyoshi Terauchi et al. and U.S. Pat. No. 4,642,034 issued on Feb. 10, 1987 to Kiyoshi Terauchi, the pair of holes provides controlled communication to an intermediate chamber. In the compressors disclosed in these patents, axial tip seal elements are located along the axial ends of the wrap elements and have been placed in direct contact with facing end surface of the end plate of the opposing scroll. Also, the pairs of holes have been located and sized so that the tip seals do not pass over the edge of the holes.
The use of anti-wear plates to cover the end plate of a scroll member in a scroll type compressor, for the purpose of reducing friction between an axial tip-seal and the end plate, has also been disclosed in the prior art, e.g., in Japanese Utility Model Application Publication No. 56-147386. However, this prior art use of an antiwear plate was in a fixed displacement compressor without displacement adjusting holes. The inventors of the present application have experimented with the use of anti-wear plates in a variable displacement compressor such as shown in FIGS. 8, 9 and 10. The inventors discovered certain problems with the anti-wear plate constructions illustrated in FIGS. 8, 9 and 10, as discussed below, and overcame these problems with the anti-wear plate construction of the present invention.
Referring to FIG. 8, a portion of a scroll compressor with a displacement adjustment mechanism is illustrated. A plurality of holes, one of which, 275a is illustrated, are formed by drilling into end plate from the side opposite from which spiral element 272 extends. The holes are drilled at positions which overlap with the inner wall of spiral element 272 so that portions of the inner wall of spiral element 272 are removed.
A seal element 213 is placed in groove 283 in the axial end surface of spiral element 282 and forms an axial seal between the spiral element 282 and the front end surface of the end plate 271. The axial end surface of spiral element 282 is also provided with a seal element which forms an axial seal between the spiral element 272 and the front end surface of the other end plate. An anti-wear plate 38 is disposed on the front end surface of end plate 271.
Referring to FIGS. 8 and 9, the configuration of anti-wear plate 38 is shown. Anti-Wear plate 38 has a plurality of cut-out portions 305a', 305b', 306a' and 306b', each of which is located adjacent to and faces a respective one of the holes, such as hole 275a seen in FIG. 8. The configuration of each cut-out portion is semicircular. FIG. 8 illustrates the scroll members in the position when spiral element 282 completely overlaps each of the holes. In this position the top or deepest portion of each semicircular cut-out portion, which is illustrated in the sectional view of FIG. 8, is located such that the whole width of seal element 213 is exposed to the hole at the top of the cut-out, and a substantial portion of the tip seal overlaps the hole inward of the remaining portion of the cut-out.
The anti-wear plate disclosed in FIG. 8 prevents friction between the seal element and front surface of the end plate. However, since a substantial part of seal element extends over the hole by passing over the semi-circular edge of the cut-out portion of antiwear plate, the seal element 213 tends to be bent toward hole 275a by high gas pressure of the fluid pockets which enters the gap between tip seal 213 and the walls of groove 283. The bending action is, particularly severe at the holes which are located in position nearest the scroll center. As a result the seal element is cut off by the edge of the cut-out portions of the anti-wear plate.
FIG. 10, illustrates an anti-wear plate construction which was tested to prevent above mentioned seal element cutting problem. In this construction, each semicircular cut-out portion of anti-wear plate 38 extends over more than a half of the width of the tip seal, i.e., past the radial center 215 of the seal element. But in this construction, the open area of the hole is decreased by the portion of the anti-wear plate extending over the hole. Pressure loss is thus increased when the compressor displacement is reduced by allowing fluid flow through the holes. As a result power consumption is increased.